There are many known applications for optical scanners for reading encoded data. One exemplary field of commercial application is that of data processing in connection with supply, storage and sale of manufactured goods. Inventory control for goods in warehouses and retail outlets is an important application of optical scanners in automatic data processing. A specific application and the one for which the subject invention was developed is that of automated checkstands in retail stores, especially grocery stores. Other known applications of optical scanners for encoded data symbols include document control, mail sorting and rail car identification. This invention was developed initially for application to automated checkstands, i.e., the so-called "point of sale" data processing for retail stores and the description will be given with respect to embodiments adapted therefor; however, as the description proceeds it will be apparent that the invention is useful in a wide variety of optical scanning applications.
There have been several proposals for machine reading of encoded labels on individual articles of merchandise at the point of sale in retail stores. A system has been proposed which includes an optical scanner situated at a checkstand so that an encoded label on each article is scanned as the article is passed over the counter surface of the checkstand. Many difficulties have been encountered in the practical realization of such a system. These difficulties have centered around the need for a code symbol which can be mass-produced with a high degree of reliability at low cost and around the need for machine reading of the code symbol regardless of its orientation on the checkstand counter by apparatus which can be feasibly installed in the checkstand of a supermarket. These needs may be characterized as the "mass producible code symbol" and the "omnidirectional code reader."
The mass-producible code symbol and the omnidirectional code reader for point of sale installation pose requirements which tend to be conflicting, if not incompatible. The omnidirectional reading requirement, which arises from the allowance of random orientation of the code symbol, is susceptible to solution by use of a code symbol of circular format. However, the requirement for a mass-producible code symbol is best satisfied by conventional printing techniques and a code symbol of circular format does not lend itself to high speed, close tolerance printing. On the other hand, the well known bar code symbol which may take the form of multiple parallel lines of varying width, does lend itself to high speed, close tolerance printing because of its incremental character; however, the bar code format has posed great difficulty with respect to the requirement of omnidirectional reading.
In the background of this invention is the adoption by the Uniform Products Code Council of a machine readable code symbol for the Grocery Industry Universal Products Code (UPC). This UPC symbol has been presented as a standard for use in automated checkstands in grocery stores in the United States. This standard symbol is of bar code format, as will be described below, and hence is suitable to high volume, close tolerance printing. Its success in practical applications insofar as technology is concerned, will depend upon the availability of feasible omnidirectional code readers. This need has been the principal stimulus in the conception and development of this invention. This invention, which is fully described hereinbelow, provides an optical scanning method and apparatus which has omnidirectional reading capability especially well suited for a code symbol of bar code format.